UNIVERSITI TEKNIKAL MALAYSIA MELAKA (UTeM)

WEAR BEHAVIOR AND CORROSION RESISTANCE OF NICKEL

COATINGS ELECTRODEPOSITED ON ALUMINUM ALLOY 7075

SUBSTRATE VIA VARIOUS CURRENT DENSITY

Report is submitted in accordance with requirement of the Universiti Teknikal Malaysia

Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering (Engineering

Materials) (Hons.)

by

SAIFUL AZHAN BIN MD ZAHIR

B051110070

910614-02-5353

FACULTY OF MANUFACTURING ENGINEERING

2015

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: Wear Behavior And Corrosion Resistance of Nickel Coatings Electrodeposited on Aluminum Alloy 7075 Substrate Via Various Current Density

SESI PENGAJIAN: 2014/15 Semester 2 Saya SAIFUL AZHAN BIN MD ZAHIR mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pertukaran antara institusi pengajian tinggi.

4. **Sila tandakan ( )

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia sebagaimana yang termaktub dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap:

No 8 Kg Petani Mukim Guar Kepayang

06700 Pendang

Kedah

Tarikh: 29th June 2015

Disahkan oleh:

Cop Rasmi: Tarikh: _______________________

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

DECLARATION

I hereby declare this report entitled WEAR BEHAVIOR AND CORROSION

RESISTANCE OF NICKEL COATINGS ELECTRODEPOSITED ON

ALUMINUM ALLOY 7075 SUBSTRATE VIA VARIOUS CURRENT DENSITY is

the result of my own research except as cited in the references.

Signature : …………………………………….

Author’s Name : SAIFUL AZHAN BIN MD ZAHIR

Date : 2th July 2015

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial

fulfillment of the requirement for the degree of Bachelor of Manufacturing Engineering

(Engineering Materials) (Hons.). The member of the supervisory is as follow:

…………………………………..

(Official Stamp of Principal Supervisor)

…………………………………..

(Official Stamp of Co-Supervisor)

i

ABSTRAK

Lapisan nikel telah dienapkan atas aloi aluminium 7075 (AA7075) melalui ketumpatan

arus. Tujuan kajian ini adalah untuk menentukan sifat haus dan ketahanan kakisan salutan

nikel yang telah dienapkan pada AA7075. Proses pengenapan ini menggunakan larutan

Watt nikel pada suhu 40 oC dan nilai pH 3.0. Pelbagai ketumpatan arus telah digunakan

iaitu 2.5, 5.0, 7.5, 10.0, dan 12.5 mA/cm2. Di antara ketiga-tiga jenis ketumpatan arus, 7.5

mA/cm2 memberikan hasil salutan yang terbaik. Morfologi salutan dianalisa

menggunakan mikroskop imbasan electron (SEM) dan komposisi salutan telah

dikenalpasti menggunakan x-ray pendafluoran (XRF). Morfologi dan struktur salutan

nikel menjadi lebih padat dan tumpat seiring dengan peningkatan ketumpatan arus.

Meningkatkan ketumpatan arus juga dapat memperbaiki saiz bijian. Sifat haus, dan

kakisan bertambah baik dengan peningkatan ketumpatan arus.

ii

ABSTRACT

The nickel coatings are electrodeposited on aluminum alloy 7075 (AA7075) via various

current density. The aim of this research is to determine the wear behavior and corrosion

resistance of nickel coating electrodeposited on AA7075 substrate. The electrodeposition

process was using a nickel Watt’s bath as a solution at a temperature of 400C and pH value

of 3.0. Various current density have been used which are 2.5, 5.0, and 7.5 mA/cm2.

Amongs these three type of current density, 7.5 mA/cm2 give the best results of

coatings.The morphology of the coating are analyzed using scanning electron microscopy

(SEM) and the composition of coatings was identified using x-ray fluorescence (XRF).

The morphologies and structures of nickel coatings become more compact and denser as

well as increasing in current density. Increasing the current density also refining the grain

size. The wear, and corrosion resistance of coating improved with the increasing in current

density.

iii

DEDICATION

This report is lovingly dedicated to my respective parents; Mr. Md Zahir Bin Zakaria and

Mrs. Zaharah Binti Mohamad Jusoh, my supervisor; Dr. Intan Sharhida Binti Othman and

Dr. Muhammad Zaimi Bin Zainal Abidin, my family’s members and also to all my friends

who have been supported and inspired me through this project.

iv

ACKNOWLEDGEMENT

Alhamdulillah, first of all, I would like to extend my gratitude to Allah S.W.T for blessing

me with health, love, opportunity and mercy to complete this research.

Besides that, I would like to extend my sincere gratitude to my supervisor, Dr. Intan

Sharhida Binti Othman who had given me guidance and support during the whole research

period. My sincere thanks also goes to Dr. Muhammad Zaimi Bin Zainal Abidin as my

co-suppervisor for his invaluable opinions during the research. Not to be forgotten, I

would like to thanks to other lecturers, laboratories staffs, friends and inviduals who,

directly or indirectly, give contribution towards my research progress.

Last but not least, I would like to thanks to my parents who always stand by my side to

give moral support and never forget to pray for me. Further, I want to acknowledge UTeM

especially Faculty of Manufacturing Engineering for giving me opportunity to gain

experience and knowledge during this four year of my study.

v

TABLE OF CONTENT

ABSTRAK i

ABSTRACT ii

DEDICATION iii

ACKNOWLEDGEMENT iv

TABLE OF CONTENT v

LIST OF TABLES viii

LIST OF FIGURES ix

LIST OF ABBREVIATIONS AND NOMENCLATURE xi

CHAPTER 1: INTRODUCTION

1.1 Background of Project 1 1.2 Problem Statement 2 1.3 Objectives 3 1.4 Scope of Project 3

CHAPTER 2: LITERATURE REVIEW

2.1 Electrodeposition of Nickel 4

2.1.1 Introduction 4

2.1.2 Method of Electrodeposition 5

2.1.3 Factor Influencing the Properties of Electrodeposited Material 6

vi

2.1.3.1 Nickel Solution 6

2.1.3.2 pH Solution 7

2.1.3.3 Temperature 8

2.1.3.4 Effect of Current Density on the Grain Size of Nickel 9

2.1.4 Application of NC-Ni Coating 11

2.2 Aluminum Alloy 7075 (AA7075) 11

2.2.1 Introduction 11

2.2.2 Type of Aluminum Alloys 12

2.2.3 Temper AA7075 13

2.2.4 Application of AA7075 14

2.3 Wear Properties of Coating 15

2.3.1 Introduction 15

2.3.2 Factor That Influence the Wear Behavior of Coating 15

2.3.2.1 Effect of Current Density 15

2.4 Corrosion of the Coating 17

2.4.1 Introduction 17

2.4.2 Factor That Influence the Corrosion Behavior 17

2.4.2.1 Effect of Current Density 17

CHAPTER 3: METHODOLOGY

3.1 Introduction 19

3.2 Sample Preparation 21

3.3 Acetone Clean 21

3.4 Hydrochloric Acid Etching 22

3.5 Electrodeposition Process of Nickel Coatings 23

3.5.1 Solution Preparation 23

vii

3.5.2 Current Density 24

3.5.3 Procedure 25

3.6 Testing & Characteristic Technique 27

3.6.1 Surface Morphology 27

3.6.1.1 X-Ray Fluorescence (XRF) 27

3.6.1.2 Scanning Electron Microscopy (SEM) 28

3.6.2 Corrosion Test 30

3.6.3 Wear Test 31

CHAPTER 4: RESULT AND DISCUSSION

4.1 Introduction 32

4.2 Nickel Coating Samples Characterization 32

4.2.1 X-Ray Fluorescence (XRF) 32

4.2.2 Scanning Electron Microscopy (SEM) 33

4.3 Nickel Coating Samples Testing 38

4.3.1 Corrosion Test 38

4.3.2 Wear Test 40

CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1 Conclusion 42

5.2 Recommendation 43

REFERENCES 44

APENDICES

viii

LIST OF TABLE

2.1 Chemical composition of AA7075 12

2.2 Mechanical properties of AA7075 12

2.3 Type of AA7075 with mechanical properties. 14

3.1 Nickel Watts’s bath solution 24

3.2 Data for current used in electrodeposition process 25

3.3 Parameter used in electrodeposition process. 26

4.1 Results of corrosion test 39

4.2 Results of wear test 40

ix

LIST OF FIGURE

2.1 Electrolytic cell for the deposition of nickel from nickel sulphate 5

solution.

2.2 XRD patterns of nickel deposits from Watts plating solutions with 7

pH values of (a) 3.8; (b) 5.0; (c) 5.5; and (d) 6.0, each at 30 min

plating time

2.3 SEM micrographs of Ni–Co–W coatings produced at (a) 2.5mA/cm2, 9

(b) 5 mA/cm2, (c) 7.5 mA/cm2, (d) 15 mA/cm2, (e) 50 mA/cm2

and (f) 70 mA/cm2

2.4 Variation of grain size of Ni deposits as a function of current density 10

2.5 SEM images nickel coatings (a, d) 90 µm grain size (b, e) 62 nm 16

grain size (c, f) 13nm grain size

2.6 Polarizing curves obtained for the alloy coatings in a 3% NaCl 18

solution; (a) NC Zn–17Ni alloy, (b) NC Zn–12Ni alloy, (c) NC

Zn–14Ni alloy, (d) NC Zn–13Ni alloy, and (e) microcrystalline

Zn–18Ni alloy

x

3.1 Research methodology flowchart 20

3.2 Samples of AA7075 21

3.3 Process of hydrochloric acid etching 23

3.4 Electrodeposition process for nickel coating 26

3.5 X-ray fluorescence machine used for composition analysis 28

(KKTM Masjid Tanah)

3.6 Scanning electron microscopy provided in the lab 29

3.7 Three electrode system glass cell used for corrosion test 30

3.8 Ball-on-disk wear test. 31

4.1 Comparison the presence of nickel before and after coating 33

4.2 SEM image of nickel coating electrodeposited on AA7075 34

substrate with various current density: (a) 2.5 mA/cm2,

(b) 5.0 mA/cm2, (c) 7.5 mA/cm2

4.3 SEM image cross-sectional view of Ni coating electrodeposited 36

on AA7075 substrate with various current density:

(a) 2.5 mA/cm2, (b) 5.0 mA/cm2, (c) 7.5 mA/cm2

4.4 Comparison of coating thickness based on different current 37

density: (a) 2.5 mA/cm2, (b) 5.0 mA/cm2, (c) 7.5 mA/cm2

4.5 Corrosion test result for bare AA7075, coatings with 2.5 mA/cm2, 38

5.0mA/cm2, and 7.5mA/cm2 respectively.

4.6 Comparison of coefficient of friction between different current 41

density of coatings

xi

LIST OF ABBREVIATIONS AND NOMENCLATURE

AA7075 - Aluminum Alloy 7075

PVD - Physical Vapor Deposition

CVD - Chemical Vapor Deposition

HVOF - High-Velocity Oxygen Fuel

NaCl - Sodium Chloride

HCl - Hydrochloric Acid

XRF - X-Ray Fluorescence

XRD - X-Ray Diffraction

SEM - Scanning Electron Microscopy

Icorr - Corrosion current

Ecorr - Corrosion potential

1

CHAPTER 1

INTRODUCTION

1.1 Background of Project

Aluminum alloy 7075 (AA7075) is commonly used as a structural material in aircraft

application due to their attractive properties that have high strength to weight ratio.

AA7075 have chemical composition roughly of zinc (Zn) 5.1-6.1 wt. %, magnesium (Mg)

2.1-2.9 wt. %, copper (Cu) 1.2-2.0 wt. %, and chromium (Cr) 0.18-0.28 wt. %. However,

this material has a problem where it has low corrosion resistance. Therefore, to overcome

this problem, a coating system has been introduced to the AA7075 in order to prevent

corrosion.

There are various techniques of coating which can be applied to AA7075 substrate, such

as electrodeposition, ion implantation, laser beam deposition, chemical vapor deposition

(CVD), physical vapor deposition (PVD), plasma and high-velocity oxygen fuel (HVOF).

Among these techniques, electrodeposition has been identified as the most economical

and superior techniques and technologically feasible with low residual porosity for

production of nickel coating. Electrodeposition have various advantages such as, low cost

and industrial applicability, can be easily control, and versatility and also has high

production rates.

2

Further, nickel has been chosen as coating material in order to improve the corrosion

resistance of AA7075. Moreover, nickel not only have good corrosion resistance but also

high melting point, strength, and ductility.

This research aims to improve the corrosion resistance of AA7075 as well as the wear

behaviors of the nickel coatings electrodeposited on AA7075 substrate. In order to get a

good result for wear behavior, the grain size of nickel coating needs to be refined by

increase the current density. Current density plays an important role on the modification

of the grain size of electrodeposited coating. The grain size of the coating can be refined

by applying a high current density during the electrodeposition process. The decreasing

of the grain size of the coatings occur rapidly by increasing the current density (Rashidi

and Amadeh, 2008).

The samples will be tested in several ways in order to determine the wear and corrosion

behavior. Ball-on-disc wear tester will be used to determine the wear behavior. The

corrosion test will be carried out by immersing the coating in a 3.5 wt. % of NaCl solution

at room temperature.

1.2 Problem Statement

AA7075 is a type of material that can easily undergo corrosion process. Thus, this alloy

needs to be coated with a coating system in order to prevent the corrosion. Previously in

aircraft industry, cadmium (Cd) or chromium (Cr) were widely used as a coating material.

However, these coatings materials are hazardous and contain a carcinogenic element

which can cause cancer.

Due to this problem, Cd and Cr are replaced with others coatings materials such as

polycrystalline nickel (Ni), nickel phosphorous (Ni-P), and zinc (Zn), even though the

properties of these materials are not as good as Cd and Cr in term of wear and corrosion

resistance.

3

One of the way to achieve a better wear resistance, and good corrosion resistance is by

decreasing the grain size of nickel coatings. Therefore, this research is focused on

increasing the surface properties of coatings by refining the grain size. According to El-

Sherik and Erb (1997), the wear properties of nickel coating are influenced by the grain

size of the coating. The challenge in this study is to produce coatings which can overcome

the low wear and corrosion resistance of AA7075. In this research, the effect of the various

current density applied in the electrodeposition process to the grain size of nickel coating

will be studied.

1.3 Objectives

1. To produce nickel coatings electrodeposited on AA7075 substrate using various

current density.

2. To analyse the corrosion resistance of nickel coatings electrodeposited on AA7075

substrate.

3. To determine the wear behavior of nickel coatings electrodeposited on AA7075

substrate.

1.4 Scope of Project

The focus of this study is to determine the wear behavior and corrosion resistance of nickel

coating electrodeposited on AA7075 substrate. The coating process will be using

electrodeposition method with suitable parameter such as current density. The function of

current density is to control the grain size of nickel coating. After that, the samples will

be test by using wear and corrosion testing. Finally, the result will be analyzed.

4

CHAPTER 2

LITERATURE REVIEW

2.1 Electrodeposition of Nickel

2.1.1 Introduction

Electrodeposition also known as electroplating is a process that using electrical current to

reduce cations of desired material from a solution and deposits as a thin film onto a

conductive substrate surface. Nickel electrodeposition is similar to other electrodeposition

processes that deposits a thin layer of nickel onto a conductive substrate. Generally, the

purpose of the nickel layer can make changes to the characteristics of a surface which are

to improved appearance, corrosion resistance, wear resistance, or other desired properties.

Nickel electrodeposition process is carried out in a solution bath which is Watts’s solution.

5

2.1.2 Method of Electrodeposition

This process used a power supply to supplies a direct current that flow between two

electrodes which are anode and cathode that immersed in conductive solution. The flow

of direct current causes the anode electrodes to dissolve and the cathode electrode to

become cover with nickel. In nickel solution contains positively charged nickel ions

(cations) and negatively charged sulphate ions (anions). When current flows, the cations

migrate to the cathode where they are discharged and deposited as metallic nickel,

(Schlesinger and Paunovic, 2010).

Figure 2.1: Electrolytic cell for the deposition of nickel from nickel sulphate solution.

6

2.1.3 Factor Influencing the Properties of Electrodeposited Material

2.1.3.1 Nickel Solution

Professor Oliver P. Watts in the one that formulated an electrolyte in 1916 that combined

nickel sulfate, nickel chloride, along with boric acid and optimized the composition of

nickel electroplating solution, (Schlesinger and Paunovic, 2010). Nowadays, this Watts

solution is widely used and caused the development of modern nickel electrodeposition

technology.

Nickel sulphate plays an importance role in the Watts bath solution. This salt has least

expensive salt of nickel with a stable anion that is not reduced at cathode, oxidized at the

anode, or volatilized. The used of nickel sulphate now is not only to raises the limiting

cathode current density but also decreases the resistivity, thus improving plate

distribution.

On the other hand, the chloride ion is used to improve anode dissolution by reducing

polarization and also increases the conductivity of the bath. It also raises the throwing

power as a result of increasing cathode efficiency, electrolyte conductivity, and slope of

the cathode potential curve.

For boric acid, it serves as a weak buffer in a nickel solution that controlling the pH in the

cathode. Boric acid also is helpful in its smoothing action on the deposit, and very pure

with inexpensive form.

Previous studies has found that the modern Watt’s formula is more concentrated than the

original, and can be represented well by nickel sulphate (NiSO4) 240-340 g/l, nickel

chloride (NiCl2) 30-60 g/l, and Boric acid (H3BO3) 30-40 g/l, (Lowenheim and Schaefer,

1974). However, in other research difference composition of Watt’s bath was studied,

(NiSO4) 250 g/l, (NiCl2) 40 g/l, and (H3BO3) 35g/l (Hu, Lin and Wen., 1996).

7

2.1.3.2 pH Solution

Range of pH in nickel solution usually can vary from 3 to 6. Keeping the pH out of this

range might has some unwanted sequences. By increasing the pH solution, the deposition

rate of alloy and nickel increased. While, when decreasing in pH, the deposition rate will

decreased.

Figure below show the XRD patterns of the Watts Ni deposited using the plating solution

at various of pH 3.8, 5.0, 5.5, and 6.0 for 30 minutes of plating time. Based on the result

obtained, the preferred orientation of the deposits obtained in the nickel solution with pH

less than or equal 5 is Ni (200), while Ni (111) is preferred orientation of the Watts nickel

deposits when the plating solution pH is above 5 (Hu, Lin and Wen., 1996).

Figure 2.2: XRD patterns of nickel deposits from Watts plating solutions with pH values of (a)

3.8; (b) 5.0; (c) 5.5; and (d) 6.0, each at 30 min plating time (Hu, Lin and Wen., 1996).

8

2.1.3.3 Temperature

Generally, in the electroplating process, the range of temperature usually is 30 to 65 C.

But the most practical given range is 40 to 60 C which is perfect. Minimum temperature

is 40 C and below than that temperature should be avoided. If the temperature lower than

40 C, any measurable effect can be seen. According to ASTM B 343-92a, an electroplating

process is operated at a temperature between 25 to 50oC.

9

2.1.3.4 Effect of Current Density on the Grain Size of Nickel Coating

Figure 2.3: SEM micrographs of Ni–Co–W coatings produced at (a) 2.5mA/cm2, (b) 5 mA/cm2, (c) 7.5

mA/cm2, (d) 15 mA/cm2, (e) 50 mA/cm2 and (f) 70 mA/cm2 (Farzaneh, Raeissi and Golozar, 2010).